Porous materials

ABSTRACT

Porous thermoset dielectric materials having low dielectric constants useful in electronic component manufacture are provided along with methods of preparing the porous thermoset dielectric materials. Also provided are methods of forming integrated circuits containing such porous thermoset dielectric material.

This application claims the benefit of Provisional Application Ser. No.60/279,541, filed on Mar. 28, 2001.

BACKGROUND OF THE INVENTION

This invention relates generally to porous materials. In particular,this invention relates to the preparation and use of porous filmscontaining thermoset materials and having a low dielectric constant.

As electronic devices become smaller, there is a continuing desire inthe electronics industry to increase the circuit density in electroniccomponents, e.g., integrated circuits, circuit boards, multichipmodules, chip test devices, and the like without degrading electricalperformance, e.g., crosstalk or capacitive coupling, and also toincrease the speed of signal propagation in these components. One methodof accomplishing these goals is to reduce the dielectric constant of theinterlayer, or intermetal, insulating material used in the components. Amethod for reducing the dielectric constant of such interlayer, orintermetal, insulating material is to incorporate within the insulatingfilm very small, uniformly dispersed pores or voids.

Porous dielectric matrix materials are well known in the art. One knownprocess of making a porous dielectric involves co-polymerizing athermally labile monomer with a dielectric monomer to form a blockcopolymer, followed by heating to decompose the thermally labile monomerunit. See, for example, U.S. Pat. No. 5,776,990. In this approach, theamount of the thermally labile monomer unit is limited to amounts lessthan about 30% by volume. If more than about 30% by volume of thethermally labile monomer is used, the resulting dielectric material hascylindrical or lamellar domains, instead of pores or voids, which leadto interconnected or collapsed structures upon removal, i.e., heating todegrade the thermally labile monomer unit. See, for example, Carter et.al., Polyimide Nanofoams from Phase-Separated Block Copolymers,Electrochemical Society Proceedings volume 97-8, pages 32-43 (1997).Thus, the block copolymer approach provides only a limited reduction inthe dielectric constant of the matrix material.

Another known process for preparing porous dielectric materialsdisperses thermally removable particles in a dielectric precursor,polymerizing the dielectric precursor without substantially removing theparticles, followed by heating to substantially remove the particles,and, if needed, completing the curing of the dielectric material. See,for example, U.S. Pat. No. 5,700,844. In the '844 patent, uniform poresizes of 0.5 to 20 microns are achieved. However, this methodology isunsuitable for such electronic devices as integrated circuits wherefeature sizes are expected to go below 0.25 microns.

U.S. Pat. No. 6,420,441 (Allen et al.), discloses porogen particles thatare substantially compatibilized with B-staged dielectric matrixmaterials. However, this patent application does not broadly teach howto prepare porous dielectric layers containing polyarylene materials.

Polyarylenes are well known dielectric materials. For example, U.S. Pat.No. 6,093,636 (Carter et al.) discloses a method for forming anintegrated circuit containing a porous high temperature thermoset, suchas a polyarylene. Such porous thermosets are prepared by using as poreforming material highly branched aliphatic esters that have functionalgroups that are further functionalized with appropriate reactive groupssuch that the functionalized aliphatic esters are incorporated into,i.e. copolymerized with, the vitrifying polymer matrix. Suchincorporation of the pore forming material into the matrix restricts themobility of the pore forming material, i.e. incorporation prevents phaseseparation of the pore forming material from the matrix. By restrictingsuch mobility, the size of the phase-separated domains is alsorestricted. Also, the '636 patent does not teach how to prepare porousthermoset dielectric materials having a mean pore diameter ≦10 nm, suchas a diameter in the range of 0.75 to 8 nm.

International Patent Application WO 00/31183 (Bruza et al.) discloses aporous cross-linked thermoset dielectric matrix material, such as apolyarylene. This patent application discloses a number of porogens,such as solvents and polymers, particularly cross-linkable polymers.Suitable cross-linkable polymers are those that react to copolymerizewith the thermoset dielectric matrix material. Suitable polymers usefulas porogens include dendrimers, hyperbranched polymer systems andcross-linked latex particles. This patent application does not teach howto prepare porous thermoset dielectric materials having a mean porediameter ≦10 nm, such as a diameter in the range of 0.75 to 8 nm, norhow to prepare such porous materials where the porogens aresubstantially free of aggregation or agglomeration and withoutcopolymerization with the dielectric matrix materials.

Other methods of preparing porous dielectric materials are known, butsuffer from broad distributions of pore sizes, too large pore size, suchas greater than 20 microns, or technologies that are too expensive forcommercial use, such as liquid extractions under supercriticalconditions.

There is thus a need for improved porous thermoset dielectric matrixmaterials with substantially smaller pore sizes and a greater percent byvolume of pores for use in electronic components, and in particular, asan interlayer, or intermetal, dielectric material for use in thefabrication of integrated circuits. There is also a need for porousthermoset dielectric materials where the volume fraction of pores in thefilm is equivalent to the volume fraction of pore forming material.

SUMMARY OF THE INVENTION

It has now been surprisingly found that certain polymeric particles (orporogens) incorporated into thermoset dielectric matrix provide porousfilms having a suitable dielectric constant and sufficiently small poresize for use as insulating material in electronic devices such asintegrated circuits and printed wiring boards. Such polymeric particlesprovide thermoset dielectric matrix material having a greater percentageof pores by volume and more uniformly dispersed pores than are availablefrom known approaches.

In a first aspect, the present invention is directed to a method ofpreparing porous thermoset dielectric materials including the steps of:a) dispersing a plurality of removable cross-linked polymeric porogenparticles in B-staged thermoset dielectric matrix material; b) forming afilm of the B-staged thermoset dielectric matrix material; c) curing theB-staged thermoset dielectric matrix material to form a thermosetdielectric matrix material; and d) subjecting the thermoset dielectricmatrix material to conditions which at least partially remove theporogen particles to form a porous thermoset dielectric material withoutsubstantially degrading the thermoset dielectric material; wherein thethermoset dielectric material is selected from the group consisting ofbenzocyclobutenes and polyarylenes; wherein the porogen particles aresubstantially compatible with the B-staged thermoset dielectric matrixmaterial and wherein the porogen particles include as polymerized unitsone or more monomers selected from the group consisting of N-vinylmonomers and heteroatom-substituted styrene monomers and at least one(meth)acrylate cross-linking agent.

In a second aspect, the present invention is directed to porousthermoset dielectric materials prepared by the method described above.

In a third aspect, the present invention is directed to a method ofpreparing an integrated circuit including the steps of: a) depositing ona substrate a layer of a composition including B-staged thermosetdielectric matrix material having a plurality of cross-linked polymericporogen particles dispersed therein; b) curing the B-staged thermosetdielectric matrix material to form a thermoset dielectric matrixmaterial; c) subjecting the thermoset dielectric matrix material toconditions which at least partially remove the porogen particles to forma porous thermoset dielectric material layer without substantiallydegrading the thermoset dielectric material; d) patterning the thermosetdielectric layer; e) depositing a metallic film onto the patterneddielectric layer; and f) planarizing the film to form an integratedcircuit; wherein the thermoset dielectric material is selected from thegroup consisting of benzocyclobutenes and polyarylenes; wherein theporogen particles are substantially compatible with the B-stagedthermoset dielectric matrix material and wherein the porogen particlesinclude as polymerized units one or more monomers selected from thegroup consisting of N-vinyl monomers and heteroatom-substituted styrenemonomers and at least one (meth)acrylate cross-linking agent.

In a fourth aspect, the present invention is directed to an integratedcircuit prepared by the method described above.

In a fifth aspect, the present invention is directed to a compositionincluding B-staged thermoset dielectric matrix material and a pluralityof cross-linked polymeric porogen particles; wherein the thermosetdielectric material is selected from the group consisting ofbenzocyclobutenes and polyarylenes; wherein the porogen particles aresubstantially compatible with the B-staged thermoset dielectric matrixmaterial and wherein the porogen particles include as polymerized unitsone or more monomers selected from the group consisting of N-vinylmonomers and heteroatom-substituted styrene monomers and at least one(meth)acrylate cross-linking agent.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout this specification, the following abbreviations shallhave the following meanings, unless the context clearly indicatesotherwise: ° C.=degrees centigrade; μm =micron=micrometer;UV=ultraviolet; rpm revolutions per minute; nm=nanometer; cm=centimeter,g=gram; wt %=weight percent; L=liter; mL=milliliter; STY=styrene;NVP=N-vinyl-pyrrolidone; NVPIM=N-vinylphthalimide;TMPTA=trimethylolpropane triacrylate; TMPTMA=trimethylolpropanetrimethacrylate; 4FSTY=4-fluorostyrene; and VAS=4-vinylanisole.

The term “(meth)acrylic” includes both acrylic and methacrylic and theterm “(meth)acrylate” includes both acrylate and methacrylate. Likewise,the term “(meth)acrylamide” refers to both acrylamide andmethacrylamide. “Alkyl” includes straight chain, branched and cyclicalkyl groups. The term “porogen” refers to a pore forming material, thatis a polymeric material or particle dispersed in a dielectric materialthat is subsequently removed to yield pores, voids or free volume in thedielectric material. Thus, the terms “removable porogen,” “removablepolymer” and “removable particle” are used interchangeably throughoutthis specification. The terms “pore,” “void” and “free volume” are usedinterchangeably throughout this specification. “Cross-linker” and“cross-linking agent” are used interchangeably throughout thisspecification and refer to a monomer containing two or morepolymerizable sites, such as double or triple bonds. “Polymer” refers topolymers and oligomers, and also includes homopolymers and copolymers.The terms “oligomer” and “oligomeric” refer to dimers, trimers,tetramers and the like. “Monomer” refers to any ethylenically oracetylenically unsaturated compound capable of being polymerized. Suchmonomers may contain one or more double or triple bonds. “Halo” refersto fluoro, chloro, bromo and iodo. Likewise, “halogenated” refers tofluorinated, chlorinated, brominated and iodinated.

The term “B-staged” refers to uncured thermoset dielectric matrixmaterials. By “uncured” is meant any thermoset material that can bepolymerized or cured to form higher molecular weight materials, such ascoatings or films. Such B-staged material may be monomeric, oligomericor mixtures thereof. B-staged material is further intended to includemixtures of polymeric material with monomers, oligomers or a mixture ofmonomers and oligomers. “Polyarylene” as used herein is intended todescribe a wide variety of thermosetting resins or polymers havingbackbones containing arylene units. Such polyarylenes includepolyarylene ethers.

Unless otherwise noted, all amounts are percent by weight and all ratiosare by weight. All numerical ranges are inclusive and combinable in anyorder, except where it is obvious that such numerical ranges areconstrained to add up to 100%.

The present invention relates to the synthesis, composition, size,distribution and purity of polymer particles useful as removableporogens, i.e., pore forming material. Such porogens are useful forforming porous thermoset dielectric materials in the fabrication ofelectronic and optoelectronic devices.

The present invention relates to a method of preparing porous thermosetdielectric materials including the steps of: a) dispersing a pluralityof removable cross-linked polymeric porogen particles in B-stagedthermoset dielectric material to form B-staged thermoset dielectricmatrix material; b) forming a film of the B-staged thermoset dielectricmatrix material; c) curing the B-staged thermoset dielectric matrixmaterial to form a thermoset dielectric matrix material; and c)subjecting the thermoset dielectric matrix material to conditions whichat least partially remove the porogen particles to form a porousthermoset dielectric material without substantially degrading thethermoset dielectric material; wherein the thermoset dielectric materialis selected from the group consisting of benzocyclobutenes andpolyarylenes; wherein the porogen particles are substantially compatiblewith the B-staged thermoset dielectric matrix material and wherein theporogen particles include as polymerized units one or more monomersselected from the group consisting of N-vinyl monomers andheteroatom-substituted styrene monomers and at least one (meth)acrylatecross-linking agent.

The porogens of the present invention are useful in reducing thedielectric constant of thermoset dielectric materials, particularlythose materials having low dielectric constants (“k”). A low-kdielectric material is any material having a dielectric constant lessthan about 4.

Thermoset dielectric materials useful in the present invention includebenzocyclobutenes, polyarylenes and mixtures thereof. Polyarylenesinclude polyarylene ethers. Suitable benzocyclobutenes include, but arenot limited to, those disclosed in U.S. Pat. Nos. 4,540,763 and4,812,588. A particularly suitable benzocyclobutene is1,3-bis(2-bicyclo[4.2.0]octa-1,3,5-trien-3-ylethynyl)-1,1,3,3-tetramethyldisiloxane,sold under the tradename CYCLOTENE by the Dow Chemical Company (Midland,Mich.).

A wide variety of polyarylenes and polyarylene ethers may be used in thepresent invention. Suitable polyarylenes may be synthesized fromprecursors such as ethynyl aromatic compounds of the formula:

wherein each Ar is an aromatic group or inertly-substituted aromaticgroup: each R is independently hydrogen, an alkyl, aryl orinertly-substituted alkyl or aryl group; L is a covalent bond or a groupwhich links one Ar to at least one other Ar; n and m are integers of atleast 2; and q is an integer of at least 1. As such, the ethynylaromatic compounds of the invention typically have four or more ethynylgroups (for example, tetraethynyl aromatic compounds) and are useful asmonomers in the preparation of polymers,. including their oligomericprecursors.

In another aspect, the polyarylenes used in the invention may include apolymer including as polymerized units:

wherein Ar′ is the residual of the reaction of product of (C≡C)_(n)-Aror Ar-(C≡C)_(m) moieties and R, L, n and m are as defined above.

In another embodiment, the polyarylene copolymers of the inventioninclude as polymerized units a monomer having the formula:

wherein Ar′ and R are as defined above.

Exemplary polyarylenes include, but are not limited to, those whereinAr-L-Ar are: biphenyl; 2,2-diphenyl propane; 9,9′-diphenyl fluorene;2,2-diphenyl hexafluoro propane; diphenyl sulfide; oxydiphenylene;diphenyl ether; bis(phenylene)diphenylsilane; bis(phenylene) phosphineoxide; bis(phenylene)benzene; bis(phenylene)naphthalene;bis(phenylene)enthracene; thiodiphenylene; 1,1,1-triphenyleneethane;1,3,5-triphenylenebenzene; 1,3,5-(2-phenylene-2-propyl)benzene;1,1,1-triphenylenemethane; 1,1,2,2-tetraphenylene- 1,2-diphenylethane;bis(1,1-diphenyleneethyl)benzene;2,2′-diphenylene-1,1,1,3,3,3-hexafluoropropane;1,1-diphenylene-1-phenylethane; naphthalene; anthracene; orbis(phenylene)napthacene; more preferably biphenylene; naphthylene;p,p′(2,2-diphenylene propane) (i.e., —C₆H₄—C(CH₃)₂—C₆H₄-);p,p′-(2,2-diphenylene-1,1,1,3,3,3-hexafluoropropene) and(—C₆H₄—C(CF₃)₂—C₆H₄—).

Useful bis-phenyl derivatives include 2,2-diphenyl propane;9,9′-diphenyl fluorene; 2,2-diphenyl hexafluoro propane; diphenylsulfide; diphenyl ether; bis(phenylene)diphenylsilane;bis(phenylene)phosphine oxide; bis(phenylene)benzene;bis(phenylene)naphthalene; bis(phenylene)anthracene; orbis(phenylene)napthacene.

The ethynyl groups on each Ar are either on adjacent carbon atoms or arevinylogously conjugated within the ring. It is believed that theydimerize upon application of heat to form an aromatic ring having a1,4-diradical which serves to polymerize and/or cross-link the compound.While not being bound by theory, it is believed that this dimerizationoccurs via Bergman cyclization such as disclosed by Warner, et al. inScience, 268, Aug. 11, 1995, pp. 814-816.

The ethynyl aromatic monomer precursors to thermosetting polyarylenesare preferably bis(o-diethynyl) monomers (also referred to as BODA(bis(ortho-diacetylene)monomers)), which means there are at least twosets of adjacent substituted or vinylogously conjugated ethynyl groupson the monomer, that is, at least one set of ethynyl groups on each Argroup. Preferably, the ethynyl aromatic compound contains from 2 to 4,most preferably 2 or 3, diethynyl sets, most preferably, except whenadditional cross-linking is desired, two sets (i.e., four) of ethynylgroups.

The polyarylene precursor monomers may be prepared by a variety ofmethods known in the art, such as by: (a) selectively halogenating,preferably in a solvent, a polyphenol (preferably a bisphenol) toselectively halogenate, preferably brominate, each phenolic ring withone halogen on one of the two positions ortho to the phenolic hydroxylgroup; (b) converting the phenolic hydroxyl on the resultingpoly(ortho-halophenol), preferably in a solvent, to a leaving group suchas a sulfonate ester (for example, a trifluoromethanesulfonate esterprepared from trifluoromethanesulfonyl halide or trifluoromethanesulfonic acid anhydride) which is reactive with and replaced by terminalethynyl compounds; and (c) reacting the reaction product of step (b)with an ethynyl-containing compound or an ethynyl synthon in thepresence of an aryl ethynylation, preferably palladium, catalyst and anacid acceptor to simultaneously replace the halogen and thetrifluoromethylsulfonate with an ethynyl-containing group (for example,acetylene, phenylacetylene, substituted phenylacetylene or substitutedacetylene). Further explanation of this synthesis is provided in PCTpatent application WO 97/10193 (Babb).

The ethynyl aromatic monomers of Formula (I) are useful to preparepolymers of either Formula (II) or (III). While not being bound bytheory, it is believed that the ethynyl groups, specifically those ofortho orientation, on the aromatic ring cyclize upon heating, forming adehydro aromatic ring which reacts to form a polymer chain. Monomerswith more than two ortho ethynyl groups (that is, more than one set ofethynyl groups) are used to form thermoset polymers and depending on theconcentration of monomer having more than one set of ortho-ethynylgroups may contain from almost none (that is, a polymer havingessentially repeat units of Formula (II) only to substantial segments oflinear polymer chain structure (that is, a polymer of Formula (III)).

Polymerization of the ethynyl aromatic monomers is well within theability of one skilled in the art. Typically, polymerization is achievedthermally and will generally occur at a temperature more than 150° C.,but polymerization temperatures are preferably at least 180° C., andmore preferably at least 210° C. The polymerization temperaturepreferably does not exceed that temperature which would result inundesirable degradation of the resulting polymer, which meanspolymerization is generally conducted at a temperature less than 300° C.for monomers having benzylic hydrogen atoms, and, for monomers nothaving a benzylic hydrogen, less than 450° C., preferably less than 400°C., and more preferably less than 350° C. The polymerization temperaturewill vary with Ar-L-Ar and R, with smaller R groups like H generallyrequiring lower temperatures than larger R groups, and more conjugatedAr and R (when aromatic) groups requiring lower temperatures than lessconjugated Ar and R groups. For example, when R or Ar is anthracene, thepolymerization is more advantageously conducted at a lower temperaturethan when Ar or R is phenyl. Polymerization is conveniently conducted atatmospheric pressure, but pressures higher or lower than atmosphericpressure can be employed.

The polymerization may be conducted in the presence of agents forcontrolling (accelerating) the cyclization reaction such as free radicalinitiators, or the chlorides disclosed by Warner, et al. in Science 269,pp. 814-816 (1995) can be employed in the polymerization reaction. Whilethe specific conditions of polymerization are dependent on a variety offactors including the specific ethynyl aromatic monomer(s) beingpolymerized and the desired properties of the resulting polymer, ingeneral, the conditions of polymerization are detailed in PCTapplication WO 97/10193 (Babb).

Particularly suitable polyarylenes for use in the present inventioninclude those sold as SiLK™ Semiconductor Dielectric (available from TheDow Chemical Company), FLARE™ dielectric (available from Honeywell), andVELOX™ poly(arylene ether) (available from Air Products/Shumacher).Other particularly suitable polyarylenes include those disclosed in WO00/31183, WO 98/11149, WO 97/10193, WO 91/09081, EP 755 957, and U.S.Pat. Nos. 5,115,082; 5,155,175; 5,179,188; 5,874,516; and 6,093,636, allherein incorporated by reference to the extent they teach polyarylenethermosets.

It will be appreciated that a mixture of dielectric materials may beused in the present invention, such as two or more thermoset dielectricmaterials or a mixture of a thermoset dielectric material with one ormore other dielectric materials, i.e. not a thermoset dielectricmaterial. Suitable other dielectric materials include, but are notlimited to, inorganic materials such as organo polysilicas, carbides,oxides, nitrides and oxyfluorides of silicon, boron, or aluminum; andorganic matrix materials such as poly(aryl esters), poly(ether ketones),polycarbonates, polynorbomenes, poly(arylene ethers),poly(perfluorinated hydrocarbons) such as poly(tetrafluoroethylene), andpolybenzoxazoles. Thus, the porogens of the present invention may becombined with a thermoset/other dielectric material mixture to form athermoset/other dielectric matrix composite material.

The porogen polymers of the present invention are cross-linked particlesand have a molecular weight or particle size suitable for use as amodifier in advanced interconnect structures in electronic devices.Typically, the useful mean particle size range for a plurality of theseparticles for such applications is up to about 1,000 nm, such as thathaving a mean particle size in the range of about 0.75 to about 1000 nm.It is preferred that the mean particle size is in the range of about0.75 to about 200 nm, more preferably from about 0.75 to about 50 nm,and most preferably from about 1 nm to about 20 nm. An advantage of thepresent process is that the size of the pores formed in the dielectricmatrix are substantially the same size, i.e., dimension, as the size ofthe removed porogen particles used. Thus, the porous dielectric materialmade by the process of the present invention has substantially uniformlydispersed pores with substantially uniform pore sizes having a mean poresize in the range of from 0.75 to 1000 nm, preferably 0.75 to 200 nm,more preferably 0.75 and 50 nm and most preferably 1 to 20 nm.Particularly suitable pore sizes are ≦10 nm, such as ≦5 nm, ≦3 nm and ≦2nm.

The cross-linked polymeric porogens include as polymerized units atleast one monomer selected from N-vinyl monomers andheteroatom-substituted styrene monomers. N-vinyl monomers suitable foruse in the present invention include, but are not limited to:vinylpyridines such as 2-vinylpyridine or 4-vinylpyridine; (C₁-C₈)alkylsubstituted N-vinyl pyridines such as 2-methyl-5-vinyl-pyridine,2-ethyl-5-vinylpyridine, 3-methyl-5-vinylpyridine,2,3-dimethyl-5-vinyl-pyridine, and 2-methyl-3-ethyl-5-vinylpyridine;N-vinylcaprolactam; N-vinylbutyrolactam; N-vinylpyrrolidone; vinylimidazole; N-vinyl carbazole; N-vinyl-succinimide; N-vinyl-oxazolidone;N-vinylphthalimide; N-vinyl-pyrrolidones such asN-vinyl-thio-pyrrolidonc, 3-methyl-1-vinyl-pyrrolidone,4-methyl-1-vinyl-pyrrolidone, 5-methyl-1-vinyl-pyrrolidone,3-ethyl-1-vinyl-pyrrolidone, 3-butyl-1-vinyl-pyrrolidone,3,3-dimethyl-1-vinyl-pyrrolidone, 4,5-dimethyl-1-vinyl-pyrrolidone,5,5-dimethyl-1-vinyl-pyrrolidone, 3,3,5-trimethyl-1-vinyl-pyrrolidone,4-ethyl-1-vinyl-pyrrolidone, 5-methyl-5-ethyl-1-vinyl-pyrrolidone and3,4,5-trimethyl-1-vinyl-pyrrolidone; vinyl pyrroles; vinyl anilines; andvinyl piperidines. Preferred N-vinyl monomers are N-vinylpyrrolidone andN-vinylphthalimide.

Heteroatom-substituted styrene monomers useful in the present inventionare any styrene monomers having one or more of the aromatic hydrogensreplaced with a heteroatom-containing substituent. Suitableheteroatom-containing substituents include, but are not limited to,(C₁-C₁₀)alkoxy, halo, amino, (C₁-C₁₀)alkylamino, di(C₁-C₁₀)alkylamino,nitro, cyano, carboxy, halo(C₁-C₁₀)alkyl, carb(C₁-C₁₀)alkoxy and thelike. Exemplary heteroatom-substituted styrene monomers include, but arenot limited to, vinylanisole, o-, m-, or p-aminostyrene,4-fluorostyrene, 3-fluorostyrene, vinyldimethoxybenzene, and the like.Preferred heteroatom substituted styrene monomers are vinylanisole, ando-, m-, or p-aminostyrene, and more preferably vinylanisole.

The amount of N-vinyl monomers or heteroatom-substituted styrenemonomers of the present invention is typically from about 1 to about 99%wt, based on the total weight of the monomers used. It is preferred thatthese monomers are present in an amount of from 1 to about 90% wt, andmore preferably from about 5 to about 90% wt. It will be appreciatedthat a mixture of N-vinyl monomers and heteroatom-substituted styrenemonomers may be used in the present porogens.

In addition to the N-vinyl monomers or heteroatom-substituted styrenemonomers, the present porogens may further contain as polymerized unitsone or more ethylenically or acetylenically unsaturated monomers,including, but not limited to, (meth)acrylic acid, (meth)acrylamides,alkyl (meth)acrylates, alkenyl (meth)acrylates, aromatic(meth)acrylates, vinyl aromatic monomers, nitrogen-containing compounds,substituted ethylene monomers, and poly(alkylene oxide) monomers.

Typically, the alkyl (meth)acrylates useful in the present invention are(C₁-C₂₄)alkyl (meth)acrylates. Suitable alkyl (meth)acrylates include,but are not limited to, “low cut” alkyl (meth)acrylates, “mid cut” alkyl(meth)acrylates and “high cut” alkyl (meth)acrylates.

“Low cut” alkyl (meth)acrylates are typically those where the alkylgroup contains from 1 to 6 carbon atoms. Suitable low cut alkyl(meth)acrylates include, but are not limited to: methyl methacrylate(“MMA”), methyl acrylate, ethyl acrylate, propyl methacrylate, butylmethacrylate (“BMA”), butyl acrylate (“BA”), isobutyl methacrylate(“IBMA”), hexyl methacrylate, cyclohexyl methacrylate, cyclohexylacrylate and mixtures thereof.

“Mid cut” alkyl (meth)acrylates are typically those where the alkylgroup contains from 7 to 15 carbon atoms. Suitable mid cut alkyl(meth)acrylates include, but are not limited to: 2-ethylhexyl acrylate(“EHA”), 2-ethylhexyl methacrylate, octyl methacrylate, decylmethacrylate, isodecyl methacrylate (“IDMA”, based on branched(C₁₀)alkyl isomer mixture), undecyl methacrylate, dodecyl methacrylate(also known as lauryl methacrylate), tridecyl methacrylate, tetradecylmethacrylate (also known as myristyl methacrylate), pentadecylmethacrylate and mixtures thereof. Particularly useful mixtures includedodecyl-pentadecyl methacrylate (“DPMA”), a mixture of linear andbranched isomers of dodecyl, tridecyl, tetradecyl and pentadecylmethacrylates; and lauryl-myristyl methacrylate (“LMA”).

“High cut” alkyl (meth)acrylates are typically those where the alkylgroup contains from 16 to 24 carbon atoms. Suitable high cut alkyl(meth)acrylates include, but are not limited to: hexadecyl methacrylate,heptadecyl methacrylate, octadecyl methacrylate, nonadecyl methacrylate,cosyl methacrylate, eicosyl methacrylate and mixtures thereof.Particularly useful mixtures of high cut alkyl (meth)acrylates include,but are not limited to: cetyl-eicosyl methacrylate (“CEMA”), which is amixture of hexadecyl, octadecyl, cosyl and eicosyl methacrylate; andcetyl-stearyl methacrylate (“SMA”), which is a mixture of hexadecyl andoctadecyl methacrylate.

The mid-cut and high-cut alkyl (meth)acrylate monomers described aboveare generally prepared by standard esterification procedures usingtechnical grades of long chain aliphatic alcohols, and thesecommercially available alcohols are mixtures of alcohols of varyingchain lengths containing between 10 and 15 or 16 and 20 carbon atoms inthe alkyl group. Examples of these alcohols are the various Zieglercatalyzed ALFOL alcohols from Vista Chemical company, i.e., ALFOL 1618and ALFOL 1620, Ziegler catalyzed various NEODOL alcohols from ShellChemical Company, i.e. NEODOL 25L, and naturally derived alcohols suchas Proctor & Gamble's TA-1618 and CO-1270. Consequently, for thepurposes of this invention, alkyl (meth)acrylate is intended to includenot only the individual alkyl (meth)acrylate product named, but also toinclude mixtures of the alkyl (meth)acrylates with a predominant amountof the particular alkyl (meth)acrylate named.

The alkyl (meth)acrylate monomers useful in the present invention may bea single monomer or a mixture having different numbers of carbon atomsin the alkyl portion. Also, the (meth)acrylamide and alkyl(meth)acrylate monomers useful in the present invention may optionallybe substituted. Suitable optionally substituted (meth)acrylamide andalkyl (meth)acrylate monomers include, but are not limited to:hydroxy(C₂-C₆)alkyl (meth)acrylates, dialkylamino(C₂-C₆)alkyl(meth)acrylates, dialkylamino(C₂-C₆)alkyl (meth)acrylamides.

Useful substituted alkyl (meth)acrylate monomers are those with one ormore hydroxyl groups in the alkyl radical, especially those where thehydroxyl group is found at the β-position (2-position) in the alkylradical. Hydroxyalkyl (meth)acrylate monomers in which the substitutedalkyl group is a (C₂-C₆)alkyl, branched or unbranched, are preferred.Suitable hydroxyalkyl (meth)acrylate monomers include, but are notlimited to: 2-hydroxyethyl methacrylate (“HEMA”), 2-hydroxyethylacrylate (“HEA”), 2-hydroxypropyl methacrylate, 1-methyl-2-hydroxyethylmethacrylate, 2-hydroxy-propyl acrylate, 1-methyl-2-hydroxyethylacrylate, 2-hydroxybutyl methacrylate, 2-hydroxybutyl acrylate andmixtures thereof.

Other substituted (meth)acrylate and (meth)acrylamide monomers useful inthe present invention are those with a dialkylamino group ordialkylaminoalkyl group in the alkyl radical. Examples of suchsubstituted (meth)acrylates and (meth)acrylamides include, but are notlimited to: dimethylaminoethyl methacrylate, dimethylaminoethylacrylate, N,N-dimethylaminoethyl methacrylamide,N,N-dimethyl-aminopropyl methacrylamide, N,N-dimethylaminobutylmethacrylamide, N,N-di-ethylaminoethyl methacrylamide,N,N-diethylaminopropyl methacrylamide, N,N-diethylaminobutylmethacrylamide, N-(1,1-dimethyl-3-oxobutyl) acrylamide,N-(1,3-diphenyl-1-ethyl-3-oxobutyl) acrylamide,N-(1-methyl-1-phenyl-3-oxobutyl) methacrylamide, and 2-hydroxyethylacrylamide, N-methacrylamide of aminoethyl ethylene urea, N-methacryloxyethyl morpholine, N-maleimide of dimethylaminopropylamine and mixturesthereof.

Other substituted (meth)acrylate monomers useful in the presentinvention are silicon-containing monomers such as γ-propyltri(C₁-C₆)alkoxysilyl (meth)acrylate, γ-propyl tri(C₁-C₆)alkylsilyl(meth)acrylate, γ-propyl di(C₁-C₆)alkoxy(C₁-C₆)alkylsilyl(meth)acrylate, γ-propyl di(C₁-C₆)alkyl(C₁-C₆)alkoxysilyl(meth)acrylate, vinyl tri(C₁-C₆)alkoxysilyl (meth)acrylate, vinyldi(C₁-C₆)alkoxy(C₁-C₆)alkylsilyl (meth)acrylate, vinyl(C₁-C₆)alkoxydi(C₁-C₆)alkylsilyl (meth)acrylate, vinyltri(C₁-C₆)alkylsilyl (meth)acrylate, and mixtures thereof.

The vinylaromatic monomers useful as unsaturated monomers in the presentinvention include, but are not limited to: styrene (“STY”),α-methylstyrene, vinyltoluene, p-methylstyrene, ethylvinylbenzene,vinylnaphthalene, vinylxylenes, and mixtures thereof.

Substituted ethylene monomers useful as unsaturated monomers is in thepresent invention include, but are not limited to: vinyl acetate, vinylformamide, vinyl chloride, vinyl fluoride, vinyl bromide, vinylidenechloride, vinylidene fluoride and vinylidene bromide.

Suitable poly(alkylene oxide) monomers include, but are not limited to,poly(propylene oxide) monomers, poly(ethylene oxide) monomers,poly(ethylene oxide/propylene oxide) monomers, poly(propylene glycol)(meth)acrylates, poly(propylene glycol) alkyl ether (meth)acrylates,poly(propylene glycol) phenyl ether (meth)acrylates, poly(propyleneglycol) 4-nonylphenol ether (meth)acrylates, poly(ethylene glycol)(meth)acrylates, poly(ethylene glycol) alkyl ether (meth)acrylates,poly(ethylene glycol) phenyl ether (meth)acrylates,poly(propylene/ethylene glycol) alkyl ether (meth)acrylates and mixturesthereof. Preferred poly(alkylene oxide) monomers includetrimethoylolpropane ethoxylate tri(meth)acrylate, trimethoylolpropanepropoxylate tri(meth)acrylate, poly(propylene glycol) methyl etheracrylate, and the like. Particularly suitable poly(propylene glycol)methyl ether acrylate monomers are those having a molecular weight inthe range of from about 200 to about 2000. The poly(ethyleneoxide/propylene oxide) monomers useful in the present invention may belinear, block or graft copolymers. Such monomers typically have a degreeof polymerization of from about 1 to about 50, and preferably from about2 to about 50.

Typically, the amount of such additional monomers useful in the porogenparticles of the present invention is from about 1 to about 99% wt,based on the total weight of the monomers used. The amount of suchadditional monomers is preferably from about 2 to about 90% wt, and morepreferably from about 5 to about 80% wt.

The porogen particles of the present invention also contain aspolymerized units one or more cross-linking agents. At least onecross-linking agent is a (meth)acrylate cross-linking agent. Suitable(meth)acrylate cross-linkers useful in the present invention includedi-, tri-, tetra-, or higher multi-functional (meth)acrylate unsaturatedmonomers. Examples of (meth)acrylate cross-linkers useful in the presentinvention include, but are not limited to: ethyleneglycol diacrylate,trimethylolpropane triacrylate, allyl methacrylate (“ALMA”),ethyleneglycol dimethacrylate (“EGDMA”), diethyleneglycol dimethacrylate(“DEGDMA”), propyleneglycol dimethacrylate, propyleneglycol diacrylate,trimethylolpropane trimethacrylate (“TMPTMA”), glycidyl methacrylate,2,2-dimethylpropane-1,3-diacrylate, 1,3-butylene glycol diacrylate,1,3-butylene glycol dimethacrylate, 1,4-butanediol diacrylate,diethylene glycol diacrylate, diethylene glycol dimethacrylate,1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, tripropyleneglycol diacrylate, triethylene glycol dimethacrylate, tetraethyleneglycol diacrylate, polyethylene glycol 200 diacrylate, tetraethyleneglycol dimethacrylate, polyethylene glycol dimethacrylate, ethoxylatedbisphenol A diacrylate, ethoxylated bisphenol A dimethacrylate,polyethylene glycol 600 dimethacrylate, poly(butanediol) diacrylate,pentaerythritol triacrylate, trimethylolpropane triethoxy triacrylate,glyceryl propoxy triacrylate, pentaerythritol tetraacrylate,pentaerythritol tetramethacrylate, dipentaerythritolmonohydroxypentaacrylate, and mixtures thereof.

One or more additional cross-linking agents may be combined with the(meth)acrylate cross-linking agent. A wide variety of cross-linkingagents may suitable be combined with the (meth)acrylate cross-linker.Such additional cross-linking agents include, but are not limited to,trivinylbenzene, divinyltoluene, divinylpyridine, divinylnaphthalene,divinylxylene, diethyleneglycol divinyl ether, trivinylcyclohexane,divinyl benzene, divinylsilane, trivinylsilane, dimethyldivinylsilane,divinylmethylsilane, methyltrivinylsilane, diphenyldivinylsilane,divinylphenylsilane, trivinylphenylsilane, divinylmethylphenylsilane,tetravinylsilane, dimethylvinyldisiloxane, poly(methylvinylsiloxane),poly(vinylhydrosiloxane), poly(phenylvinylsiloxane), tetraallylsilane,1,3-dimethyl tetravinyldisiloxane, 1,3-divinyl tetramethyldisiloxane andmixtures thereof.

The (meth)acrylate cross-linking agents and additional cross-linkingagents may be used in a wide range of amounts, such as from 1 to 99%,based on the total weight of monomers and cross-linking agents. It ispreferred that the amount of cross-linking agent is from 5 to 95%, morepreferably from 8 to 90%, and still more preferably from 10 to 50%.

In general, suitable B-staged thermoset dielectric materials useful inthe present invention have a molecular weight of less than or equal toabout 100,000. Preferably, the molecular weight of the B-stagedthermoset dielectric material is from about 1000 to about 50,000, andmore preferably from 1000 to 35,000. As the molecular weight of theB-staged dielectric material increases above about 35,000, it becomesincreasingly difficult for the porogen particles to be compatible withthe dielectric material. In cases where the molecular weight is greaterthan about 35,000, particularly greater than or equal to 50,000, it ispreferred that the N-vinyl monomers or heteroatom-substituted styrenemonomers be present in the porogen particles in an amount of at least20% based on the total weight of the monomers and cross-linker, and morepreferably greater than 20%, such as 25%, 30%, 35%, 40% and mostpreferably at least 45%. For B-staged thermoset dielectric materialshaving molecular weights greater than about 35,000, it is preferred thatthe porogen particles include N-vinylpyrrolidone as polymerized units.In addition, for such thermoset materials one or more different monomersmay also be required to compatiblize the porogen. Such monomers include,but are not limited to, vinyl benzoate, vinyl naphthalene, vinylbiphenyl and 4-allyl-2-methoxyphenol. In such cases, a (meth)acrylatecross- linking agent is still used. In an alternate embodiment, when theB-staged dielectric material is benzocyclobutene, it is preferred thatthe porogen particles include vinylanisole as polymerized units.

The polymers useful as porogen particles in the present invention may beprepared by a variety of polymerization techniques, such as solutionpolymerization or emulsion polymerization, and preferably by solutionpolymerization. The solution polymers useful in the present inventionmay be copolymers or homopolymers and are cross-linked.

The solution polymers of the present invention may be prepared by avariety of methods, such as those disclosed in U.S. Pat. No. 5,863,996(Graham) and U.S. patent application Ser. No. 09/460,326, both of whichare hereby incorporated by reference to the extent they teach thepreparation of such polymers. The solution polymers of the presentinvention are generally prepared in a non-aqueous solvent. Suitablesolvents for such polymerizations are well known to those skilled in theart. Examples of such solvents include, but are not limited to:hydrocarbons, such as alkanes, fluorinated hydrocarbons, and aromatichydrocarbons, ethers, ketones, esters, alcohols and mixtures thereof.Particularly suitable solvents include dodecane, mesitylene, xylenes,diphenyl ether, gamma-butyrolactone, ethyl lactate, propyleneglycolmonomethyl ether acetate, caprolactone, 2-hepatanone, methylisobutylketone, diisobutylketone, propyleneglycol monomethyl ether, decanol, andt-butanol.

The solution polymer porogen particles of the present inventiontypically have a weight average molecular weight in the range of 5,000to 1,000,000, preferably in the range of 10,000 to 500,000 and morepreferably in the range of 10,000 to 100,000. These solution polymerporogen particles typically have a particle size up to about 1,000 nm,such as in the range of 0.75 to 1000 nm. It is preferred that the meanparticle size of a plurality of these particles is in the range of about0.75 to about 100 nm, more preferably from about 0.75 about 50 nm, andmost preferably from about 1 nm to about 20 nm. Particularly usefulporogen particles are those having a mean particle size of <10 nm,particularly <5 nm, such as 1 nm, 2 nm or 3 nm. The polydispersity ofthese solution polymers is in the range 1 to 20 and more preferably inthe range of 1.001 to 15 and most preferably in the range of 1.001 to10.

The emulsion polymers useful in the present invention are generallyprepared the methods described in U.S. patent application Ser. No.09/460,326, described above. Controlled polymerization of the monomersin these droplets produces small polymer particles, i.e. ≦100 nm, andpreferably extremely small polymer particles, i.e. ≦50 nm in size.Emulsion polymers having other suitable mean particle sizes, such as ≦45nm, ≦40 nm, ≦35 nm, and ≦30 nm, may be produced according to the presentinvention. Such polymer particles typically have a lower mean particlesize of about 1 nm. Thus, the present polymer particles have a meanparticle size range of from 0.75 to 100 nm, and preferably from 1 to 50nm. The particle size polydispersity of these emulsion polymer particlesis in the range 1.0001 to 10, more preferably 1.001 to 5, and mostpreferably 1.001 to 2.5.

It is preferred that the polymers of the present invention are preparedusing anionic polymerization or free radical polymerization techniques.It is also preferred that the polymers useful in the present inventionare not prepared by step-growth polymerization processes.

The porogen particles of the present invention may be directly added tothe B-staged thermoset dielectric material as is or may be firstpurified to remove impurities that might effect the electrical orphysical properties of electronic devices. Purification of the porogenparticles may be accomplished either by precipitation of the porogenparticles or adsorption of the impurities.

In general, the cross-linked particles of the present invention usefulas porogens must be dispersible, miscible or otherwise substantiallycompatible with the host B-staged dielectric matrix material in solutionand in the thin film. Thus, the porogen particles must be soluble in thesame solvent or mixed solvent system as the host B-staged thermosetdielectric matrix material. Also, the porogen particles must be presentwithin this solution as substantially discrete, substantiallynon-aggregated or substantially non-agglomerated particles in order toachieve the desired benefit of this invention, namely substantiallyuniformly dispersed pores with a size comparable to that of theporogen's size. This is accomplished by modifying the porogen particlecomposition such that it is “compatible” with the host B-stagedthermoset dielectric matrix material.

It has been surprisingly found that when the present porogen particlesinclude as polymerized units at least one monomer selected from N-vinylmonomers and heteroatom-substituted styrene monomers and at least one(meth)acrylate cross-linking agent, that such porogen particles aresubstantially compatible with B-staged thermoset dielectric matrixmaterials. Such porogen particles, when added to B-staged thermosetdielectric materials, remain as substantially discrete, substantiallynon-aggregated or substantially non-agglomerated particles. In this way,porous materials are obtained containing pores having a mean porediameter substantially equal to the mean pore diameter of the porogenparticles used. Thus, very large pores, such as so-called “killerdefects or pores” obtained upon agglomeration or aggregation ofporogens, are substantially reduced or eliminated according to thepresent invention. Thus, the present invention provides porous thermosetdielectric materials having much smaller pores, more uniformly sizedpores and more uniformly dispersed pores than conventional methods.

An advantage of the present invention is that the porogen particles aresubstantially compatible, and preferably fully compatible, with thedielectric material used. By “compatible” is meant that a composition ofB-staged thermoset dielectric matrix material and a plurality of porogenparticles are optically transparent to visible light. It is preferredthat a solution of B-staged thermoset dielectric matrix material andporogen particles, a film or layer including a composition of B-stagedthermoset dielectric material and porogen particles, a compositionincluding B-staged thermoset dielectric matrix material having porogenparticles dispersed therein, and the resulting porous dielectricmaterial after removal of the porogen particles are all opticallytransparent to visible light. By “substantially compatible” is meantthat a composition of B-staged polyimide dielectric matrix material anda plurality of porogen particles is slightly cloudy or slightly opaque.Preferably, “substantially compatible” means at least one of a solutionof B-staged thermoset dielectric matrix material and porogen particles,a film or layer including a composition of B-staged thermoset dielectricmatrix material and porogen particles, a composition including B-stagedthermoset dielectric matrix material having porogen particles dispersedtherein, and the resulting porous thermoset dielectric material afterremoval of the porogen particles is slightly cloudy or slightly opaque.

To be compatible, the porogen particles must be soluble or miscible inthe B-staged thermoset dielectric matrix material, in the solvent usedto dissolve the B-staged thermoset dielectric matrix material or both.When a film or layer of a composition including the B-staged thermosetdielectric material, a plurality of porogen particles and solvent iscast, such as by spin casting, much of the solvent evaporates. Aftersuch film casting, the porogen particles must be soluble in the B-stagedthermoset dielectric matrix material so that it remains substantiallyuniformly dispersed. If the porogen particles are not compatible, phaseseparation of the porogen particles from the B-staged thermosetdielectric matrix material occurs and large domains or aggregates form,resulting in an increase in the size and non-uniformity of pores. Suchcompatible porogen particles provide cured dielectric materials havingsubstantially uniformly dispersed pores having substantially the samesizes as the porogen particles.

The compatibility of the porogen particles and B-staged thermosetdielectric matrix material is typically determined by a matching oftheir solubility parameters, such as the Van Krevelen parameters ofdelta h and delta v. See, for example, Van Krevelen et al., Propertiesof Polymers. Their Estimation and Correlation with Chemical Structure,Elsevier Scientific Publishing Co., 1976; Olabisi et al.,Polymer-Polymer Miscibility, Academic Press, N.Y., 1979; Coleman et al.,Specific Interactions and the Miscibility of Polymer Blends, Technomic,1991; and A. F. M. Barton, CRC Handbook of Solubility Parameters andOther Cohesion Parameters, 2^(nd) Ed., CRC Press, 1991. Delta h is ahydrogen bonding parameter of the material and delta v is a measurementof both dispersive and polar interaction of the material. Suchsolubility parameters may either be calculated, such as by the groupcontribution method, or determined by measuring the cloud point of thematerial in a mixed solvent system consisting of a soluble solvent andan insoluble solvent. The solubility parameter at the cloud point isdefined as the weighted percentage of the solvents. Typically, a numberof cloud points are measured for the material and the central areadefined by such cloud points is defined as the area of solubilityparameters of the material.

When the solubility parameters of the porogen particles and B-stagedthermoset dielectric matrix material are substantially similar, theporogen particles will be compatible with the dielectric matrix materialand phase separation and/or aggregation of the porogen particles is lesslikely to occur. It is preferred that the solubility parameters,particularly delta h and delta v, of the porogen particles and B-stagedthermoset dielectric matrix material are substantially matched. It willbe appreciated by those skilled in the art that the properties of theporogen particles that affect the particles' solubility also affect thecompatibility of these particles with the B-staged thermoset dielectricmatrix material. It will be further appreciated by those skilled in theart that porogen particles may be compatible with one thermosetdielectric matrix material, but not another. This is due to thedifference in the solubility parameters of the different B-stagedthermoset dielectric matrix materials.

To be useful as porogen particles in forming porous dielectricmaterials, the porogens of the present invention must be at leastpartially removable under conditions which do not adversely affect thedielectric matrix material, preferably substantially removable, and morepreferably completely removable. By “removable” is meant that thepolymer depolymerizes or otherwise breaks down into volatile componentsor fragments which are then removed from, or migrate out of, thedielectric material yielding pores or voids. Any procedures orconditions which at least partially remove the porogen without adverselyaffecting the dielectric matrix material may be used. It is preferredthat the porogen is substantially removed. Typical methods of removalinclude, but are not limited to, exposure to heat or radiation, such as,but not limited to, UV, x-ray, gamma ray, alpha particles, neutron beamor electron beam. It is preferred that the matrix material is exposed toheat or UV light to remove the porogen.

The porogen particles of the present invention can be thermally removedunder vacuum, nitrogen, argon, mixtures of nitrogen and hydrogen, suchas forming gas, or other inert or reducing atmosphere. The porogenparticles of the present invention may be removed at any temperaturethat is higher than the thermal curing temperature of the B-stagedthermoset matrix material and lower than the thermal decompositiontemperature of the thermoset dielectric material. Typically, the porogenparticles of the present invention may be removed at temperatures in therange of 150° to 500° C. and preferably in the range of 250° to 450° C.Typically, the porogen particles of the present invention are removedupon heating for a period of time in the range of 1 to 120 minutes. Anadvantage of the porogens of the present invention is that 0 to 20% byweight of the porogen remains after removal from the thermosetdielectric material.

In one embodiment, when a porogen of the present invention is removed byexposure to radiation, the porogen polymer is typically exposed under aninert atmosphere, such as nitrogen, to a radiation source, such as, butnot limited to, visible or ultraviolet light. The porogen fragmentsgenerated from such exposure are removed from the matrix material undera flow of inert gas. The energy flux of the radiation must besufficiently high to generate a sufficient number of free radicals suchthat porogen particle is at least partially removed. It will beappreciated by those skilled in the art that a combination of heat andradiation may be used to remove the porogens of the present invention.

In preparing the dielectric matrix materials of the present invention,the porogen particles described above are first dispersed within, ordissolved in, a B-staged thermoset dielectric material. Any amount ofporogen particles may be combined with the B-staged thermoset dielectricmatrix materials according to the present invention. The amount ofporogen particles used will depend on the particular porogen employed,the particular B-staged thermoset dielectric matrix material employed,and the extent of dielectric constant reduction desired in the resultingporous dielectric material. Typically, the amount of porogen particlesused is in the range of from 1 to 90 wt %, based on the weight of theB-staged thermoset dielectric matrix material, preferably from 10 to 80wt %, more preferably from 15 to 60 wt %, and still more preferably from15 to 30 wt %. A particularly useful amount of porogen is in the rangeof form about 1 to about 60 wt %.

The porogen particles of the present invention may be combined with theB-staged thermoset dielectric material by any methods known in the art.Typically, the B-staged thermoset material is first dissolved in asuitable solvent, such as, but not limited to, methyl isobutyl ketone,diisobutyl ketone, 2-heptanone, γ-butyrolactone, ε-caprolactone, ethyllactate propyleneglycol monomethyl ether acetate, propyleneglycolmonomethyl ether, diphenyl ether, anisole, n-amyl acetate, n-butylacetate, cyclohexanone, N-methyl-2-pyrrolidone,N,N′-dimethylpropyleneurea, mesitylene, xylenes, or mixtures thereof, toform a solution. The porogen particles are then dispersed or dissolvedwithin the solution. The resulting dispersion is then deposited on asubstrate by methods known in the art, such as spin coating, spraycoating or doctor blading, to form a film or layer.

After being deposited on a substrate, the B-staged thermoset dielectricmatrix material is then substantially cured to form a film, layer orcoating. The dielectric matrix material is typically cured by heating ata temperature below that required for removal of the porogen. Suitablecure temperatures for the B-staged thermoset dielectric matrix materialvary across a wide range but are generally from about 150° to about 455°C., preferably from about 200° to about 400° C.

Once the B-staged thermoset dielectric matrix material is cured, thefilm is subjected to conditions which remove the porogen particleswithout substantially degrading the polyimide dielectric material, thatis, less than 5% by weight of the dielectric material is lost.Typically, such conditions include exposing the film to heat and/orradiation. It is preferred that the material is exposed to heat or lightto remove the porogen. To remove the porogen particles thermally, thedielectric material can be heated by oven heating or microwave heating.Under typical thermal removal conditions, the polymerized dielectricmaterial is heated to about 300° to about 450° C. It will be recognizedby those skilled in the art that the particular removal temperature of athermally labile porogen will vary according to composition of theporogen. The choice of porogen particles will depend upon the thermaldegradation temperature of the thermoset dielectric material. Uponremoval, the porogen polymer depolymerizes or otherwise breaks down intovolatile components or fragments which are then removed from, or migrateout of, the dielectric matrix material yielding pores or voids, whichfill up with the carrier gas used in the process. Thus, a porousthermoset dielectric material having voids is obtained, where the sizeof the voids is substantially the same as the particle size of theporogen. The resulting dielectric material having voids thus has a lowerdielectric constant than such material without such voids.

The compatible, i.e., optically transparent, compositions of the presentinvention do not suffer from agglomeration or long range ordering ofporogen materials, i.e. the porogen particles are substantiallyuniformly dispersed throughout the B-staged thermoset dielectric matrixmaterial. Thus, the porous thermoset dielectric materials resulting fromremoval of the porogen particles have substantially uniformly dispersedpores. Such substantially uniformly dispersed, very small pores are veryeffective in reducing the dielectric constant of the dielectricmaterials.

A further advantage of the present invention is that low dielectricconstant materials are obtained having uniformly dispersed voids, ahigher volume of voids than known dielectric materials and/or smallervoid sizes than known dielectric materials. These voids are on the orderof 0.75 to 1000 nm, preferably 0.75 to 200 nm, more preferably 0.75 to50 nm, and most preferably 1 to 20 nm. Particularly suitable are poreshaving a mean pore size of ≦10 nm, ≦5 nm, ≦3 nm, and ≦2 nm. Further, thevoid size can be adjusted, from 1 to 1000 nm and above, by varying thesize of the removable porogen particles. The resulting porous theromosetdielectric material has low stress, less brittleness, low dielectricconstant, low refractive index, improved toughness and improvedcompliance during mechanical contacting to require less contact forceduring compression. The porogens of the present invention also act asimpact modifiers for the thermoset materials and improve thermoset filmformation as well as film properties.

The porogens of the present invention are compatible with B-stagedthermoset material without the need for further functionalization of theporogen. It is preferred that the present porogens are not furtherfunctionalized, and particularly that they are not further surfacefunctionalized. Also, the present porogens are not incorporated into thevitrifying polymer, i.e. the porogens are not copolymerized with theB-staged thermoset dielectric material. The present porogen particlesare compatibilized with the B-staged thermoset matrix material byappropriate choice of monomer, cross-linking agent or both. The presentporogens can be mixed or blended with the B-staged thermoset materialwithout macroscopic phase separation. Phase separation typically resultsin a visually detectable second layer, i.e. the compositions are opaque.The compositions of the present invention containing porogen particlesin a thermoset dielectric matrix material are substantially non-phaseseparated and preferably are not phase separated. Surprisingly, phaseseparation of the porogens is prevented according to the presentinvention by compatibilizing the porogens with the thermoset dielectricmatrix material. Such compatibilization, which is based on solubility,is achieved by choice of monomers used to prepare the porogen, not byimmobilizing (i.e. copolymerizing) the porogen in the matrix polymer.

The porous thermoset dielectric material made by the process of thepresent invention is suitable for use in any application where a lowrefractive index or low dielectric constant material may be used. Whenthe porous dielectric material of the present invention is a thin film,it is useful as insulators, anti-reflective coatings, sound barriers,thermal breaks, insulation, optical coatings and the like. The porousthermoset dielectric materials of the present invention are preferablyuseful in electronic and optoelectronic devices including, but notlimited to, the fabrication of multilevel integrated circuits, e.g.microprocessors, digital signal processors, memory chips and band passfilters, thereby increasing their performance and reducing their cost.

The porous thermoset dielectric materials of the present invention areparticularly suitable for use in integrated circuits, optoelectronicdevices and wireless devices such as mobile telephones. The presentporous thermosets are suitable used on a variety of substrates, such as,but not limited to, gallium arsenide, silicon-germanium,silicon-on-insulator, silicon, alumina, aluminum-nitride, printed wiringboards, flexible circuits, multichip modules, flip chips, copper, copperalloys, aluminum, high dielectric materials, low dielectric materials,resistors, barrier layers such as titanium or tantalum nitride, etchstop or cap layers such as silicon nitride, silicon oxide or siliconoxycarbide, and the like. It will be appreciated that an overlayer maybe applied to such porous thermosets in certain applications.

In one embodiment of integrated circuit manufacture, as a first step, alayer of a composition including B-staged thermoset dielectric matrixmaterial having a plurality of cross-linked polymeric porogen dispersedor dissolved therein and optionally a solvent is deposited on asubstrate. Suitable deposition methods include spin casting, spraycasting and doctor blading. Suitable optional solvents include, but arenot limited to: methyl isobutyl ketone, diisobutyl ketone, 2-heptanone,γ-butyrolactone, ε-caprolactone, ethyl lactate propyleneglycolmonomethyl ether acetate, propyleneglycol monomethyl ether, diphenylether, anisole, n-amyl acetate, n-butyl acetate, cyclohexanone,N-methyl-2-pyrrolidone, N,N′-dimethylpropyleneurea, mesitylene, xylenesor mixtures thereof. Suitable substrates include, but are not limitedto: silicon, silicon dioxide, silicon oxycarbide, silicon germanium,silicon-on-insulator, glass, silicon nitride, ceramics, aluminum,copper, gallium arsenide, plastics, such as polycarbonate, circuitboards, such as FR-4 and polyimide, and hybrid circuit substrates, suchas aluminum nitride-alumina. Such substrates may further include thinfilms deposited thereon, such films including, but not limited to: metalnitrides, metal carbides, metal silicides, metal oxides, and mixturesthereof. In a multilayer integrated circuit device, an underlying layerof insulated, planarized circuit lines can also function as a substrate.

In a second step in the manufacture of integrated circuits, the B-stagedthermoset matrix material is cured to form a thermoset dielectric matrixmaterial. In a third step, the resulting cured thermoset dielectricmatrix material is then subjected to conditions such that the porogenparticles contained therein is substantially removed without adverselyaffecting the dielectric material to yield a porous thermoset dielectricmaterial.

The porous thermoset dielectric material is then lithographicallypatterned to form vias, and/or trenches in subsequent processing steps.The trenches generally extend to the substrate and connect to at leastone metallic via. Typically, lithographic patterning involves (i)coating the dielectric material layer with a positive or negativephotoresist, such as those marketed by Shipley Company (Marlborough,Mass.); (ii) imagewise exposing, through a mask, the photoresist toradiation, such as light of appropriate wavelength or e-beam; (iii)developing the image in the resist, e.g., with a suitable developer; and(iv) transferring the image through the dielectric layer to thesubstrate with a suitable transfer technique such as reactive ion beametching. Optionally, an antireflective composition may be disposed onthe dielectric material prior to the photoresist coating. Suchlithographic patterning techniques are well known to those skilled inthe art.

A metallic film is then deposited onto the patterned dielectric layer tofill the trenches. Preferred metallic materials include, but are notlimited to: copper, tungsten, gold, silver, aluminum or alloys thereof.The metal is typically deposited onto the patterned dielectric layer bytechniques well known to those skilled in the art. Such techniquesinclude, but are not limited to: chemical vapor deposition (“CVD”),plasma-enhanced CVD, combustion CVD (“CCVD”), electro and electrolessdeposition, sputtering, or the like. Optionally, a metallic liner, suchas a layer of nickel, tantalum, titanium, tungsten, or chromium,including nitrides or silicides thereof, or other layers such as barrieror adhesion layers, e.g. silicon nitride or titanium nitride, isdeposited on the patterned and etched dielectric material.

In a fifth step of the process for integrated circuit manufacture,excess metallic material is removed, e.g. by planarizing the metallicfilm, so that the resulting metallic material is generally level withthe patterned dielectric layer. Planarization is typically accomplishedwith chemical/mechanical polishing or selective wet or dry etching. Suchplanarization methods are well known to those skilled in the art.

It will be appreciated by those skilled in the art that multiple layersof dielectric material, including multiple layers of thermosetdielectric material, and metal layers may subsequently be applied byrepeating the above steps. The above steps in the manufacture of anelectronic device may further include one or more other steps, such as,but not limited to, the application of etch stops, cap layers, barrierlayers, seed layers and the like. It will be further appreciated bythose skilled in the art that the compositions of the present inventionare useful in any and all methods of integrated circuit manufacture.

The following examples are presented to illustrate further variousaspects of the present invention, but are not intended to limit thescope of the invention in any aspect.

EXAMPLE 1

A vinylanisole containing cross-linked porogen was prepared bypolymerizing the monomers vinylanisole/styrene/trimethylolpropanetriacrylate in a weight ratio of 45/45/10.

Approximately 2 mL of a 35 wt % solids solution of a commerciallyavailable B-staged benzocyclobutene (“BCB”) in mesitylene and 2 mL of a15 wt % solids solution of the porogen in mesitylene were combined in a20 mL vial and mixed thoroughly. The resultant pale yellow transparentsolution contained 70% BCB and 30% porogen with a total solids contentof 25%. 2 mL of the solution was disposed by a pipette onto a stationary4 inch (ca. 10 cm) wafer on a spin coater. The wafer was then spun at2500 rpm for 30 seconds and the wafer was removed and the film visuallyexamined. The BCB/porogen film was clear and free of visible defects,striations or haze. The wafer was then heated to 150° C. on a brass hotplate for 1 minute to remove excess solvent. The film was then againvisually examined and was clear and free of visible defects, striationsor haze. Thus, the porogen was compatible with the B-staged BCBdielectric material.

EXAMPLE 2

The following porogen samples were prepared by polymerizing the monomersin the amounts reported in Table 1.

TABLE 1 Porogen Sample Monomer A Monomer B Cross-linker C A/B/C A STYNVP TMPTA 45/45/10 B NVP — TMPTA 90/10 C STY NVP TMPTA 80/10/10 D STYVAS TMPTA 45/45/10 E STY NVPIM TMPTA 45/45/10 F STY 4FSTY TMPTA 80/10/10G STY VAS TMPTA 80/10/10

EXAMPLE 3

The compatibility of a number of porogen samples from Example 2 inB-staged polyarylene ether dielectric materials in cyclohexanone wasdetermined. The B-staged polyarylene ether material was either VELOX Apoly(arylene ether) (“Polyarylene ether A”) or VELOX N poly(aryleneether) (“Polyarylene ether N”), both available from AirProducts/Shumacher. Both commercially available B-staged materials had amolecular weight of approximately 50,000. Compatibility determinationswere performed by visually inspecting a film of the B-staged polyaryleneether dielectric material and porogen that was spun cast on a siliconwafer at 1000 rpm. The porogen was loaded into the B-staged polyarylenedielectric material at ca. 50% by weight with a total solids content ofca. 20%. The film thicknesses were from 0.9 to 2 μm. All visualinspections were by naked-eye under daylight. Film compatibility of theporogen in the polyarylene ether dielectric material was determinedafter removal of the solvent, but before removal of the porogen. Thecompatibility results are reported in Table 2.

TABLE 2 Porogen Film Polyarylene Ether Sample Solution CompatibilityCompatibility A A clear clear B clear clear C cloudy — N A clear clear Bclear clear C cloudy —

From these data, it can be clearly seen that Porogen Samples A and Bwere compatible with both polyarylene ether samples. Porogen Sample C,which contained the same components as Porogen Sample A, did not containa sufficient amount of NVP to compatiblize the porogen with the highmolecular weight (ca. 50,000) B-staged polyarylene ether.

1. A method of preparing an integrated circuit comprising the steps of:a) depositing on a substrate a layer of a composition comprisingB-staged thermoset dielectric matrix material having a plurality ofcross-linked polymeric porogen particles dispersed therein; b) curingthe B-staged thermoset dielectric matrix material to form a thermosetdielectric matrix material wherein the porogen particles are notcopolymerized with the B-staged thermoset dielectric matrix material; c)subjecting the thermoset dielectric matrix material to conditions whichat least partially remove the porogen particles to form a porousthermoset dielectric material layer without substantially degrading thethermoset dielectric material; d) patterning the thermoset dielectriclayer; e) depositing a metallic film onto the patterned dielectriclayer; and f) planarizing the film to form an integrated circuit;wherein the thermoset dielectric material is selected from the groupconsisting of benzocyclobutenes and polyarylenes; wherein the porogenparticles are substantially compatible with the B-staged thermosetdielectric matrix material and wherein the porogen particles comprise aspolymerized units one or more monomers selected from the groupconsisting of N-vinyl monomers and heteroatom-substituted styrenemonomers and at least one (meth)acrylate cross-linking agent.
 2. Themethod of claim 1 wherein the plurality of porogen particles has a meanparticle size of ≦10 nm.
 3. The method of claim 1 wherein the(meth)acrylate cross-linking agent is selected from the group consistingof ethyleneglycol diacrylate, trimethylolpropane triacrylate, allylmethacrylate, ethyleneglycol dimethacrylate, diethyleneglycoldimethacrylate, propyleneglycol dimethacrylate, propyleneglycoldiacrylate, trimethylolpropane trimethacrylate, glycidyl methacrylate,2,2-dimethylpropane-1,3-diacrylate, 1,3-butylene glycol diacrylate,1,3-butylene glycol dimethacrylate, 1,4-butanediol diacrylate,diethylene glycol diacrylate, diethylene glycol dimethacrylate,1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, tripropyleneglycol diacrylate, triethylene glycol dimethacrylate, tetraethyleneglycol diacrylate, polyethylene glycol 200 diacrylate, tetraethyleneglycol dimethacrylate, polyethylene glycol dimethacrylate, ethoxylatedbisphenol A diacrylate, ethoxylated bisphenol A dimethacrylate,polyethylene glycol 600 dimethacrylate, poly(butanediol) diacrylate,pentaerythritol triacrylate, trimethylolpropane triethoxy triacrylate,glyceryl propoxy triacrylate, pentaerythritol tetraacrylate,pentaerythritol tetramethacrylate, dipentaerythritolmonohydroxypentaacrylate, and mixtures thereof.
 4. The method of claim 1wherein the N-vinyl monomers are selected from the group consisting ofvinylpyridines, (C₁-C₈)alkyl substituted N-vinyl pyridines;N-vinylcaprolactam; N-vinylbutyrolactam; N-vinylpyrrolidone; vinylimidazole; N-vinyl carbazole; N-vinyl-succinimide; N-vinyl-oxazolidone;N-vinylphthalimide; N-vinyl-pyrrolidones; vinyl pyrroles; vinylanilines; and vinyl piperidines.
 5. The method of claim 1 wherein theN-vinyl monomers are selected from the group consisting ofN-vinylpyrrolidone and N-vinylphthalimide.
 6. The method of claim 1wherein the heteroatom-substituted styrene monomers are selected fromthe group consisting of vinylanisole, o- aminostyrene, m-aminostyrene,p-aminostyrene, 4-fluorostyrene, 3-fluorostyrene, andvinyldimethoxybenzene.
 7. The method of claim 1 wherein the B-stagedthermoset dielectric matrix material has a molecular weight of greaterthan 35,000 and wherein the porogen comprises N-vinylpyrrolidone aspolymerized units in an amount of at least 20%, based on the totalweight of the monomers and cross-linker.
 8. The method of claim 1wherein the B-staged thermoset dielectric matrix material isbenzocyclobutene and wherein the porogen comprises vinylanisole aspolymerized units.